An inflatable vehicle occupant protection device, such as an air bag, is inflated upon the occurrence of a vehicle crash. The air bag is part of an apparatus which further includes a crash sensor and an inflator. The crash sensor senses vehicle conditions that indicate the occurrence of a crash. When the crash sensor senses a crash-indicating condition of at least a predetermined threshold level, the inflator is actuated and emits inflation fluid which inflates the air bag into the vehicle occupant compartment. The air bag can then engage a vehicle occupant to help protect the occupant from a forceful impact with parts of the vehicle as a result of the crash.
The inflator includes a structure defining an inflation fluid pressure chamber. A closure portion of the inflator structure closes the chamber. The inflator further includes a pyrotechnic initiator which, when actuated, emits pyrotechnic combustion products that cause the closure portion of the inflator structure to rupture so that inflation fluid in the chamber can flow from the inflator to the air bag.